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The European Space Agency (ESA) describes giant elliptical galaxies as “the most puzzling type of galaxy in the universe.” Astronomers have been perplexed by these “red-and-dead” galaxies—thus named because they mysteriously stop forming stars, and the only stars that remain after they shut down are very old, low-mass, red stars.

Astronomers once thought these galaxies were dead because they lacked enough cold gas (a vital star ingredient) to produce stars. But, a recent study led by Norbert Werner from Stanford University found an abundance of cold gas in some red, dead galaxies not previously studied.

“This is bizarre: with plenty of cold gas at their disposal, why aren’t these galaxies forming stars?” asked study co-author Raymond Oonk from the Netherlands Institute for Radio Astronomy, according to an ESA report published Tuesday.

The answer may be found in a black hole.

The central supermassive black holes within these galaxies may be sucking in cold gas, which boosts their accretion rate (the rate at which they build up matter), and spewing out jets that either reheat the cold gas in the surrounding galaxy, or push it out of reach with a great force. Basically, the black holes are stirring the pot, or that’s the hypothesis.

ESA summarizes: “Jets from the central supermassive black hole heat or stir up the gas and prevent it from turning into stars.”

Werner told ESA: “These galaxies are red, but with the giant black holes pumping in their hearts, they are definitely not dead.”